Torque control strategy for management of rollback in a wheeled vehicle whose powertrain includes a rotary electric machine

Abstract

Requested brake torque and requested throttle torque are assigned opposite algebraic signs in both rollback and non-rollback states. In the non-rollback state, requested motor torque development includes a process step ( 206 ) in which requested brake torque and requested throttle torque are algebraically summed. In the rollback state, requested motor torque development includes a process step ( 218 ) in which requested throttle torque is substituted for the regeneration torque limit. In the rollback state, the difference between the requested throttle torque and the requested brake torque is compared with a zero vehicle speed regeneration torque limit ( 228 ) when the result of comparing the difference between requested throttle torque and the requested brake torque with the regeneration torque limit ( 222 ) discloses that the latter difference does not exceed the regeneration torque limit. The result is used to determine respective amounts of motor torque and friction brake torque ( 230, 232, 234, 236 ).

What is claimed is:  
     
       1. A motor vehicle comprising: 
       road-engaging wheels;  
       a powertrain comprising a rotary electric machine that is operatively coupled through a drivetrain to the road-engaging wheels and that is capable both of delivering traction torque to the wheels and of imposing regenerative braking torque on the wheels;  
       friction brakes for applying friction brake torque to the wheels;  
       a throttle request source that is selectively operable by a driver of the vehicle to request traction torque for accelerating the vehicle;  
       a brake request source that is selectively operable by the driver to request brake torque for braking the vehicle;  
       at least one processor for providing a motor torque request to the rotary electric machine and a friction brake torque request to the friction brakes by processing data that includes a request from the throttle request source and a request from the brake request source to develop a torque modification that defines an appropriate regeneration torque component of the motor torque request to the electric machine, and by also processing data that includes a request from the throttle request source and a request from the brake request source, data that defines a regeneration limit, and data that distinguishes between the vehicle being in a non-rollback state wherein the direction of vehicle motion is not contrary to that selected by a selector mechanism associated with the powertrain and the vehicle being in an incipient rollback state wherein the direction of vehicle motion is contrary to that selected by the selector mechanism, to develop the torque modification, the friction brake torque request, and a total torque that is used in subsequent processing that develops the motor torque request;  
       wherein certain change in the request from the throttle request source calling for a decrease in traction torque is effective to create corresponding compression regenerative braking torque simulating the compression braking that would occur in an internal combustion when a depressed throttle of such an engine is released;  
       wherein in both the rollback and non-rollback states, the brake torque request from the brake request source, a request from the throttle request source calling for compression regenerative braking torque, and the torque modification are assigned the same algebraic sign, and a request from the throttle request source calling for traction torque is assigned an opposite algebraic sign;  
       wherein in the non-rollback state, the at least one processor develops the total torque by the algebraic summation of the request from the brake request source and the request from the throttle request source; and  
       in the rollback state, the at least one processor develops the total torque by the subtraction of the request from the brake request source from the request from the throttle request source and sets the regeneration limit equal to the request from the throttle request source.  
     
     
       2. A motor vehicle as set forth in claim  1  in which, in the rollback state, the at least one processor causes the regeneration limit to be a value other than the value corresponding to the throttle torque request when prevailing conditions associated with regeneration call for a value of the regeneration limit lower than the value resulting from equating the regeneration limit to the throttle torque request. 
     
     
       3. A motor vehicle as set forth in claim  1  in which, in the rollback state, the at least one processor compares the total torque with the regeneration limit. 
     
     
       4. A motor vehicle as set forth in claim  3  in which, in the rollback state, the at least one processor sets the friction brake torque request equal to the difference between the total torque and the regeneration limit and sets the motor torque request equal to the regeneration limit, when the total torque exceeds the regeneration limit. 
     
     
       5. A motor vehicle as set forth in claim  3  in which, in the rollback state, the at least one processor compares total torque with a zero vehicle speed regeneration torque limit when the regeneration limit exceeds the total torque. 
     
     
       6. A motor vehicle as set forth in claim  5  in which, in the rollback state, the at least one processor sets the friction brake torque request to zero and sets the motor torque request equal to the total torque when the total torque is greater than the zero vehicle speed regeneration torque limit. 
     
     
       7. A motor vehicle as set forth in claim  5  in which, in the rollback state, the at least one processor sets the friction brake torque request equal to the total torque minus the zero vehicle speed regeneration torque limit and sets the motor torque request equal to the zero vehicle speed regeneration torque limit when the total torque is less than the zero vehicle speed regeneration torque limit. 
     
     
       8. A motor vehicle as set forth in claim  1  in which in the rollback state, the at least one processor modifies the regeneration limit by reducing the regeneration limit as a function of one or both time and vehicle speed. 
     
     
       9. A motor vehicle as set forth in claim  1  in which the at least one processor comprises plural processors, one of which develops the friction brake torque and the torque modification, and the other of which develops both the motor torque request and data defining a direction of rolling of the vehicle and supplies the data defining the direction of rolling to the one processor. 
     
     
       10. A motor vehicle as set forth in claim  1  in which the data that distinguishes between the vehicle being in a non-rollback state wherein the direction of vehicle motion is not contrary to that selected by a selector mechanism associated with the powertrain and the vehicle being in an incipient rollback state wherein the direction of vehicle motion is contrary to that selected by the selector mechanism identifies a rollback state both when the direction of vehicle motion is forward while the selector mechanism is selecting a reverse direction and when the direction of vehicle motion is backward while the selector mechanism is selecting a forward direction. 
     
     
       11. In a motor vehicle comprising: 
       road-engaging wheels;  
       a powertrain comprising a rotary electric machine that is operatively coupled through a drivetrain to the road-engaging wheels and that is capable both of delivering traction torque to the wheels and of imposing regenerative braking torque on the wheels;  
       friction brakes for applying friction brake torque to the wheels;  
       a throttle request source that is selectively operable by a driver of the vehicle to request traction torque for accelerating the vehicle;  
       a brake request source that is selectively operable by the driver to request brake torque for braking the vehicle;  
       at least one processor for providing a motor torque request to the rotary electric machine and a friction brake torque request to the friction brakes by processing data that includes a request from the throttle request source and a request from the brake request source to develop a torque modification that defines an appropriate regeneration torque component of the motor torque request to the electric machine, and by also processing data that includes a request from the throttle request source and a request from the brake request source, data that defines a regeneration limit, and data that distinguishes between the vehicle being in a non-rollback state wherein the direction of vehicle motion is not contrary to that selected by a selector mechanism associated with the powertrain and the vehicle being in an incipient rollback state wherein the direction of vehicle motion is contrary to that selected by the selector mechanism, to develop the torque modification, the friction brake torque request, and a total torque that is used in subsequent processing that develops the motor torque request;  
       wherein certain change in the request from the throttle request source calling for a decrease in traction torque is effective to create corresponding compression regenerative braking torque simulating the compression braking that would occur in an internal combustion when a depressed throttle of such an engine is released;  
       a method that comprises distinct processes for rollback and non-rollback states of the vehicle, including;  
       in both the rollback and non-rollback states, assigning the same algebraic sign to the brake torque request from the brake request source, a compression regenerative braking torque request resulting from change in the request from the throttle request source calling for a decrease in traction torque from the throttle, and the torque modification, and assigning an opposite algebraic sign to a request from the throttle request source calling for traction torque;  
       in the non-rollback state, developing the total torque by algebraically summing the request from the brake request source and the request from the throttle request source;  
       in the rollback state, developing the total torque by subtracting the request from the brake request source from the request from the throttle request source; and  
       in the rollback state, setting the regeneration limit equal to the request from the throttle request source.  
     
     
       12. A method as set forth in claim  11  including, in the rollback state, causing the regeneration limit to be a value other than the value corresponding to the throttle torque request when prevailing conditions associated with regeneration call for a value of the regeneration limit lower than the value resulting from equating the regeneration limit to the throttle torque request. 
     
     
       13. A method as set forth in claim  11  including, in the rollback state, comparing the total torque with the regeneration limit. 
     
     
       14. A method as set forth in claim  13  including, in the rollback state when the total torque exceeds the regeneration limit, setting the friction brake torque request equal to the difference between the total torque and the regeneration limit and setting the motor torque request equal to the regeneration limit. 
     
     
       15. A method as set forth in claim  13  including, in the rollback state when the regeneration limit exceeds the total torque, comparing total torque with a zero vehicle speed regeneration torque limit. 
     
     
       16. A method as set forth in claim  15  in which in the rollback state when the total torque is greater than the zero vehicle speed regeneration torque limit, setting the friction brake torque request to zero and setting the motor torque request equal to the total torque. 
     
     
       17. A method as set forth in claim  15  in which in the rollback state when the total torque is less than the zero vehicle speed regeneration torque limit, setting the friction brake torque request equal to the total torque minus the zero vehicle speed regeneration torque limit and setting the motor torque request equal to the zero vehicle speed regeneration torque limit. 
     
     
       18. A method as set forth in claim  11  in which in the rollback state, modifying the regeneration limit by reducing the regeneration limit as a function of one or both time and vehicle speed. 
     
     
       19. A method as set forth in claim  11  in which the data that distinguishes between the vehicle being in a non-rollback state wherein the direction of vehicle motion is not contrary to that selected by a selector mechanism associated with the powertrain and the vehicle being in an incipient rollback state wherein the direction of vehicle motion is contrary to that selected by the selector mechanism is developed to identify a rollback state both when the direction of vehicle motion is forward while the selector mechanism is selecting a reverse direction and when the direction of vehicle motion is backward while the selector mechanism is selecting a forward direction.